Have tried trim-pots for nulling DC-offset, but something does not add up....
I did de-solder the output-resistor, and null each chip (some variation here), checked and fine-tuned after 30min.
Then re-soldered, and now I have ~20mV ?
It seems that there is a difference when adjusting towards ground and between chips. What gives?
As mentioned...the production-spread among these chips are larger than life...

Originally posted by Cobra2
Have tried trim-pots for nulling DC-offset, but something does not add up....
I did de-solder the output-resistor, and null each chip (some variation here), checked and fine-tuned after 30min.
Then re-soldered, and now I have ~20mV ?
It seems that there is a difference when adjusting towards ground and between chips. What gives?
As mentioned...the production-spread among these chips are larger than life...

Secondly, I suspect there are some interactions between the chips. Try nulling offsets with the chips connected normally and repeat a few times while the Amp settles it's temperature. It is clear that JR does not employ Servos (he seems to share my dislike for their sound) and if he can so shall we DIY'ers.

Hey, I forgot, the OPA's are FET input I think, so you cannot null the offset the same way as on the LM3875/3886. Simply use 0.47/0.5R output resistors, ground the non-inverting input and hope for the best.

If they are not FET Input your Pot needs to be around twice the value of all the resistors that are not DC blocked on the inverting input in paralell, so in your case 6k2//220k*2 = 12k - NPV is 10k.